Asphalt manufacture

ABSTRACT

Asphalt products having improved rheological properties are prepared from asphaltic residues by means of catalytic hydrogenation under moderate conditions.

United States Patent Gordon A. MeLaren Westport, Conn.;

John W. Gibson, Oakland, Calif. 880,629

Nov. 28, 1969 Sept. 21, 1971 Shell Oil Company New York, N.Y.

Inventors App]. No. Filed Patented Assignee ASPHALT MANUFACTURE 5Claims, 1 Drawing Fig.

OTHER REFERENCES Chem. Eng. News, Vol. 34, No. 9, p. 4686- 4687, Sept.24, 1956 Primary ExaminerDelbert E. Gantz Assistant Examiner-VeronicaO'Keefe Attorney-Harold L. Denkler ABSTRACT: Asphalt products havingimproved rheological properties are prepared from asphaltic residues bymeans of catalytic hydrogenation under moderate conditions.

PATENTED SEPZ] I97! PENETRATION, DECIMILLIMETERS (IOO grams, 5 seconds,77F) IOO SLOPE X SLOPE Y I00 I000 VISCOSITY AT 275 F, SAYBOLT SECONDSFUROL INVENTORS G, A. MC LAREN 8% W- GIBSON THEIR ATTORNEY ASPHALTMANUFACTURE This invention relates to a process for producing asphaltproducts having highly desirable rheological properties from asphalticpitch by means of catalytic treatment with hydrogen.

Conventional asphalt manufacture involves the reduction of soft straightrun residues, typically having penetrations above 1,000 decimillimeters(dmm.) at 77 F., to a consistency permitting their use as asphaltproducts by vacuum flashing, solvent extraction or air blowing at anelevated temperature. In the first two of the aforementioned procedures,reduction to specification grade is accomplished by removing aproportion of the heavy oil fraction contained in the straight runresidue. In the latter process the desired consistency is obtainedthrough condensation and polymerization of the heavy oil and resinousfractions contained in the residues.

Because the heavy distillate oil fraction contained in straight runresidue is valuable, for example, as conversion feed for catalyticcracking, there has been an increasing trend toward reducing theseresidues to a hard asphaltic pitch thereby maximizing distillate oilrecovery. The resulting pitches are usually hard, relatively brittlematerials, having very low penetrations, e.g., 5 dmm. or less at 77 F.Due to their inherent physical properties, such pitches have limitedutility and are not suitable for most asphaltic applications unlessblended with a cutter stock such as a flashed distillate or other oil.Obviously, the use of such an oil or oil-containing residue forblending, frustrates the objective of maximizing the recovery ofvaluable oil fractions from the residue. Hard pitch can be disposed ofby conversion to coke for use as fuel, but this likewise is not a verysatisfactory alternative, since pitch residues frequently contain highconcentrations of sulfurous and nitrogenous compounds which when burnedresult in the release of noxious sulfur and nitrogen oxides to the air.

Therefore, there exists in the art a need for a practicable method ofconverting asphaltic pitches to useful products. The present inventionprovides such a process; a process wherein asphalt products are preparedhaving rheological properties superior to those of asphalts preparedfrom straight run residues by conventional methods of manufacture.

It has now been found that asphalt products having highly desirablerheological properties can be prepared from asphaltic pitch by means ofcatalytic hydrogenation under moderate conditions. Hydrogenation underthe conditions hereinafter described has been found to alter thechemical and physical characteristics of the pitch in such a manner asto produce products having viscosimetric properties superior to those ofasphalts prepared by conventional manufacturing techniques. In addition,it has been found that good product yields are attained at relativelylow levels of hydrogen consumption, and that good catalyst life can alsobe achieved. This latter aspect is particularly surprising consideringthe chemical nature of pitch, which in addition to containing asubstantial proportion of asphaltenes that would be expected to depositon the catalyst, also contains sizable quantities of sulfur and nitrogencompounds, and metals such as vanadium and other elements considered tobe detrimental to catalyst life.

As an additional benefit of the present process, concomitant distillateproducts are freed of a substantial proportion of heteroatoms and tracemetals. Since sulfur and nitrogen compounds and metalliferouscontaminants are relatively innocuous in asphalt, it is preferred toonly partially remove these contaminants from the residue. Metaldeposition on catalyst is thus limited thereby extending catalyst life.

The rheological properties of asphalt are generally expressed in termsof their penetration, viscosity, softening point and ductility. Theseproperties are considered indicative of the nature of the asphalt andare related to the inherent structure of bituminous materials. Asphaltsof equivalent penetration grade are not necessarily suitable for thesame application, since penetration is but one measure of the asphalt srheological properties. For example, it is known that penetrationtogether with viscosity can be used to predict the setting properties ofasphalt when hot-mixed with aggregate in paving applications. It hasbeen found through experience that asphalts of equivalent penetrationgrade will set slower or faster depending on their viscosity. Generallythose having the highest viscosity at or near the hot-mix temperaturewill have the fastest setting time and thus be the more advantageous foractual use.

A highly significant advantage of the present invention is that for agiven penetration, the asphalt products prepared by the inventiveprocedure, have appreciably greater viscosities than those produceddirectly from straight run residue by conventional vacuum flashing. Thecatalytic hydrogenation of the pitch apparently results in a molecularrearrangement which not only increases its penetration without the useof cutterstocks, but additionally imparts highly desirable viscosimetricproperties to the resulting asphalt products.

The improved viscosimetric properties of asphalts prepared in accordancewith the invention will be more readily apparent by reference to theaccompanying drawing. The drawing is a graph showing the relationshipbetween penetration and viscosity of asphalts prepared by conventionalvacuum flashing of a straight run residue (Slope X), compared with thepenetration-viscosity relationship of asphalts prepared by catalytichydrogenation of pitch (Slope Y) derived from the same straight runresidue. It is evident from the graph, that at most any givenpenetration the viscosity at 275 F of the asphalt prepared by vacuumreducing to grade, is lower than that of the asphalt prepared by theprocess of the invention, e.g., a rrb penetration grade asphalt producedby the present process has a viscosity at 275 F. of I30 S.S.F. ascompared to a viscosity of only 95 S.S.F. for the asphalt obtained byreducing straight run residue to a penetration grade. The hydrogenatedproduct would, therefore, set faster and be more desirable in pavingapplications than the conventionally prepared asphalt.

The starting material or feedstock to the process of the invention canbe any asphaltic residue of petroleum, e.g., cracked residue, straightrun residue (bottoms product from the atmospheric or vacuum distillationof crude oils), residue from solvent deasphalting processes and thelike. Such residues comprise predominantly high boiling fractions, i.e.,those fractions boiling above 650 F. of which the asphaltic (pitch)fraction generally comprises the highest boiling materials therein. Suchasphaltic pitch-containing residues can be catalytically hydrogenateddirectly and the improved asphaltic pitch fraction subsequentlyrecovered by fractionation, or if desired the residue can befractionated prior to hydrogenation to recover the distillate fractionbeforehand, in which case the feed to the process will be predominantlythe heavy pitch fraction.

Lower boiling hydrocarbon fractions can be included in the asphalticresidue feed if desired and in some cases can be quite advantageous asthe low boiling fractions tend to be a wash oil in the catalytichydrotreatment and would be improved in quality, e.g., through partialremoval of sulfur and nitrogen compounds. The process of the inventionis particularly advantageous in preparing asphalt products from hardasphaltic pitch, i.e., pitch having a penetration below about 5 dmm. at77 F. as determined by ASTM Method D5, and boiling point essentiallyabove about 900 F. Such pitch is obtained, for example, by deep flashingstraight run or cracked residue.

Catalytic hydrogenation processes in general, are well known andthoroughly described in the art, and need not be discussed in detailherein. In accordance with the an asphaltic residue feedstock issubjected to catalytic treatment with hydrogen at temperatures rangingfrom about 600 F. to about 850 F., preferably from about 675 F. to 775F., and at pressures of about 1,000 p.s.i.g. to about 5,000 p.s.i.g.,preferably 1,500 p.s.i.g. to about 3,500 p.s.i.g. The weight hourlyspace velocity can be varied from about 0.2 to about 2.0, but preferablyis maintained at about 0.5 to about 1.0. A hydrogen circulation rate ofbetween about 1,500 and 15,000 s.c.f./bbl. of pitch can be employed,more normally from about 5,000 to 10,000 a.c.f./bbl. of pitch.

Under the specified hydrogenating conditions, generally less than aboutpercent w/o and normally less than about 10 percent w/o of the feedstockis converted to products boiling below 600 F. to obtain relatively highyields of asphalt. If desired, somewhat higher conversions to lightboiling products can be obtained which are recoverable and couldsuitably be used for distillate fuels, jet fuels or other purposes.

Effluent from the catalytic hydrotreating e.g. is separated into one ormore fractions. For example, a gas phase is separated from the liquidproduct and desirably is recycled to the hydrotreating zone, with orwithout a suitable treatment to remove any undesirable impurities suchas hydrogen sulfide or ammonia. Makeup hydrogen can be added as needed.Pure hydrogen is not necessary as gases rich in hydrogen can be used,e.g., hydrogen gases produced in catalytic reforming of naphthas whichare on the order of 70 -80 percent v/o by volume of hydrogen or more,but correspondingly higher operating pressures are required to maintainadequate hydrogen partial pressures.

Liquid product from the hydrotreating zone is suitably fractionated toremove any low boiling hydrocarbons and to recover an asphalt fractionboiling essentially above about 600 F., and preferably above about 650F., and having a penetration at 77 F. of at least about dmm. higher andpreferably at least 40 dmm. higher than the corresponding asphalticfraction in the residue feed. Thus by practice of the invention asphaltproducts of most any desired penetration can be prepared from asphalticpitch or pitch-containing residues. In a preferred embodiment of theinvention hard pitch having a penetration at 77 F. of less than about 5dmm. is converted to asphalt products having penetrations of about 30 toabout 500 at 77 F. and viscosities between about 50 and about 500centistokes at 275 F.

In general, any of the catalysts conventionally employed in thehydrogenation of heavy petroleum oils can be utilized in the presentprocess. In general, the catalyst comprises a hydrogenation component ona suitable refractory oxide support. Examples of suitable catalyticcomponents are the Group VIB and Group VIII metals such as molybdenum,tungsten, chromium, cobalt, nickel, iron and their oxides and sulfides.Mixtures of these materials or compounds of two or more of the oxidescan also be employed. These catalytic components are generallycomposited, with a suitable carrier of the solid refractory type, e. g.,alumina, silica, or combinations thereof. Supports having an acidiccharacter such as silica alumina or fluorided alumina are also suitable.Especially suitable are the oxides and/or sulfides of nickel andmolybdenum on an alumina carrier. The metals are generally employed inan amount ranging from about 0.1 percent w/o to about percent w/o orhigher. The preparation of hydrogenation catalysts is well known andpracticed commercially.

The invention will be further described by means of the followingexamples which demonstrate various embodiments of the invention. Itshould be understood, however, that these examples are given forillustrative purposes only and that the invention in its broader aspectsis not limited thereto.

EXAMPLE I Flasher pitch having the properties indicated in table I washydrogenated in the presence of a commercial hydrogenation catalystunder the conditions shown in table II. The total liquid product fromeach of these runs (I-IV) was fractionated to free the asphalt productof water and light ends. The properties of the asphalt product having aboiling range above 572 F. is shown in table II, as well as productyields and percentages heteroatom and metallic contaminant removal.

TABLE I Pitch Feedstock Vacuum Flushed Straight Run Residue of u SourceHeuvy San Joaquin Valley, Califomia Crude Properties Penetration at 77F., drnmv 0-1 Viscosity at 275 F., CS 1,900 Softening Point, F, 177 FComponents boiling above 932 F, Bi-w 99.4 Sulfur, %w l .6 Nitrogen.%w 15Oxygen, 70w 1 l Iron, ppm. 195 Nickel, p.p.m. 215 Vanadium, ppm. 105

TABLE 11 l II III IV llydrogcnating conditions:

Catalyst ago M fin Ti 85 Temperature, I 725 738 752 770 Pressure,p.s.i,g V 1, 800 1, 8m) 1, 1, 800 Weight hourly sp 0. fit) (J. 5!) 0.610. 43 Ratio Ila/pitch, s.c.t,/bbl H 7, 400 f), 300 11, 800 is, 000 111consumptlon, sic.t./bbl 350 410 510 830 Total liquid product:

Percent w. yield basis feed 08. 8 us 1 17. 8 J8. 0 Percent w. productboiling below 572 F 2. 3 3. 2 5.0 f 3 Percent w. product boiling above932 F i 8) l 85, 9 82. E) T0. ll Properties of 572 F. plus asphaltproduct:

Penetration at 77 F., drnm 40 7s m0 470 Viscosity at 275 F., cs... 7 415270 21G tiii Viscosity at 140 F., poiscsnfl 4, OJO 1, 545 l, 0-10 lllliPercent w. yield basis total liquid product i 98. 21 97. 7t) 96. 16 93.31'] Removal of heteroatoms, percent w.:

Sulfur 47 57 55 (iii Nitrogen 3 r 12 20 Oxygen 4) 53 58 5!] Metalsremoval from total product,

percent w.:

Iron 92 87 N1ckel 65 57 61 Vanadium 47 67 68 lie extruded pellets ofalumina-supported nickel-molybdenum, 3% nickel, 10% molybdenum wasemployed as catalyst.

From the above data it is evident that useful asphalt products can bemanufactured from pitch without the inclusion of valuable cutter stocks.The products produced in above runs have penetrations and viscositieswithin the general range of paving grade asphalts and would be eminentlysuitable for this purpose. The above data further demonstrate thatvirtually the entire range of asphalt consistencies can be produced bycatalytic hydrotreatment of pitches, e.g. from low penetration gradeasphalts to soft fluxes. The response to penetration increase has beenfound to be more strongly dependent on temperature of the catalytichydrotreatment than on pressure. By modifying the hydrogenationtemperature and controlling the other variables, asphalt products ofmost any desired consistency can be obtained.

It is noted that the catalyst after 85 days still possessed goodactivity indicating such a catalyst can be effectively employed in thetreatment of heavy asphaltic charge stocks for relatively long periodsof service.

EXAMPLE 11 To further demonstrate the inventive process, asphalts ofvarying consistencies were prepared under the conditions and having theproperties shown in table 111. The feedstock was the same as thatofExarnple l. 7

Various modifications can be made in the procedures of the specificexamples to provide other embodiments which fall within the scope of thepresent invention. For example, while it is possible to preparepenetration grade asphalts directly from asphaltic pitch without thenecessity of employing a cutter stock, it may be desirable in someinstances to blend minor amounts of a cutter stock with the hydrogenatedasphalt products of the invention to prepare a particular penetrationgrade material. Likewise, it is understood that asphalts produced by theinventive process can be diluted with petroleum solvents to form roadcutbacks, and can also be employed in the form of an emulsion or be usedin any other application for which conventional asphalts are employed.

We claim as our invention:

1. A process for producing asphalt products from asphaltic pitch whichcomprises contacting asphaltic petroleum residue having a penetration ofless than 5 decimillimeters at 77 F. with hydrogen in the presence of ahydrogenation catalyst at a temperature in the range of from about 600F. to about 850 F F. a pressure of from about 1,000 to about 5,000pounds per square inch gauge, and recovering an asphalt having apenetration at 77 F. of about 30 to about 500 decimillimeters and aviscosity at 275 F. between about 50 and about 500 centistokes.

2. The process of claim 1 wherein the asphaltic residue is composedpredominantly of fractions boiling above 650 F.

3 The process of claim 1 wherein the catalyst comprises nickelmolybdenum supported on alumina.

4. A process for producing asphalt products from asphaltic pitch whichcomprises contacting hard asphaltic pitch having a penetration of lessthan 5 decimillimeters at 77 F. with hydrogen in the presence of anickel molybdenum supported on alumina catalyst at a temperature in therange from about 600 F. to about 850 F a pressure of from about 1,000 toabout 5,000 pounds per square inch gauge and a weight hourly spacevelocity of about 0.2 to about 2.0 and recovering an asphalt producthaving a penetration at 77 F. of about 30 to about 500 decimillimetersand a viscosity at 275 F. between about 50 and about 500 centistokes,wherein less than about 15 percent w/o of the pitch feed is converted toproducts boiling below 600 F.

5. The process of claim 4 wherein the catalytic hydrogenation isperformed at a temperature in the range of about 675 F. to about 775 F.at a pressure of about 1,500 to about 3,500 pounds per square inchgauge.

2. The process of claim 1 wherein the asphaltic residue is composedpredominantly of fractions boiling above 650* F.
 3. The process of claim1 wherein the catalyst comprises nickel molybdenum supported on alumina.4. A process for producing asphalt products from asphaltic pitch whichcomprises contacting hard asphaltic pitch having a penetration of lessthan 5 decimillimeters at 77* F. with hydrogen in the presence of anickel molybdenum supported on alumina catalyst at a temperature in therange from about 600* F. to about 850* F., a pressure of from about1,000 to about 5,000 pounds per square inch gauge and a weight hourlyspace velocity of about 0.2 to about 2.0 and recovering an asphaltproduct having a penetration at 77* F. of about 30 to about 500decimillimeters and a viscosity at 275* F. between about 50 and about500 centistokes, wherein less than about 15 percent w/o of the pitchfeed is converted to products boiling below 600* F.
 5. The process ofclaim 4 wherein the catalytic hydrogenation is performed at atemperature in the range of about 675* F. to about 775* F. at a pressureof about 1,500 to about 3,500 pounds per square inch gauge.